Runs rough at all speeds
Sounds like a complete tune-up to me...
To me that sounds like a bad coil. If you don't have a code showing you will soon. Install a whole new set of plugs if you have very many miles on the current set. Plugs are a "tuneup" on your truck! Be sure and use anti-seize on the new plug threads.
Ford = Triton = coils fail all the time.
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